Method for recording information, apparatus for recording information and information recording medium

ABSTRACT

Before original information is recorded in areas such as a recording medium management area where the same pattern of information is recorded many times, a dummy pattern that minimizes a recording film flow is recorded. Because the direction of the recording film flow depends on the length of a mark length, the dummy pattern is a pattern including marks with a unique length. Randomly or sequentially selecting and recording a plurality of dummy patterns, each with a recording film flow direction different from others, prevents jitters, which will be caused by the recording film flow, from increasing.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method and an apparatus forrecording information on an information recording medium by directing anenergy beam to the medium to melt its recording film, and to theinformation recording medium used by the method. More particularly, thepresent invention relates to a method and an apparatus for recordinginformation on phase change disks such as a DVD-RAM and a DVD-RW, and toan information recording medium used for the method.

[0002] In the description of the present invention, the informationrecording medium described above is mentioned as a phase change opticaldisk or simply as an optical disk. However, the present inventionapplies to any information recording medium on which information isrecorded by directing an energy beam to the medium to heat and melt itsrecording film in order to change the atomic arrangement. Therefore,regardless of the shape of an information recording medium, the presentinvention is applicable also to a method and an apparatus for recordinginformation on non-circular information recording media such as anoptical card, and to an information recording medium used for themethod.

[0003] In addition, the energy beam described above is sometimesmentioned simply as a laser beam or as a light. However, any energy beamcapable of generating heat on an information recording medium to meltits recording medium may be used in the present invention as describedabove. Furthermore, although a red laser (645 nm to 660 nm ofwavelength) is used in the method and the apparatus according to thepresent invention, the present invention is applicable also to ahigh-density optical disk using a relatively shorter wavelength laser,such as a blue laser and a purple laser.

[0004] Recently, phase change optical disks such as a 2.6 GB DVD-RAM,capable of reproducing information from reproduction-only optical diskssuch as a DVD-ROM or DVD-Video, have been placed on the market. However,the 2.6 GB DVD-RAM does not respond sufficiently to the consumer's needsin the recording capacity. This raises expectations for a 4.7 GB DVD-RAMor a 4.7 GB DVD-RW. That is, these phase change optical disks,equivalent to a DVD-Video in recording capacity, are available for useas video recording optical disks that will replace VTRs.

[0005] However, it has been pointed out that the recording by thephase-change recording method, if repeated several thousands to scoresof thousands times, would degrade the reproduced signal and preventinformation from being reproduced correctly (see JP-A-10-49872 disclosedon Feb. 20, 1998). The phase change recording method melts the recordingfilm during information recording. This means that the viscosity of themelted area of the recording film decreases and that the recording filmflows in some direction. This also changes the thickness in some areasin the recording film. The central level of the reproduced signal andthe amplitude depend largely on the thickness of the recording film. Asa result, a degradation that depends upon the thickness of the recordingfilm occurs in the reproduced signal, causing jitters.

[0006] To solve this problem, two information recording methods havebeen devised (Both are described in JP-A-10-49872 described above).

[0007] One method is to shift the information recording start positionby about eight bytes randomly each time information is recorded in eachsector. This method shifts each two consecutive melting parts by atleast eight bytes even if the same pattern information is recorded andtherefore minimizes the amount of recording film flow described above.The other method is to reverse the polarity of recorded information eachtime information is recorded in each sector. The optical disk systemdescribed above employs the mark edge recording method. This mark edgerecording method records marks (parts melted by a high-power pulsetrain), each having its own length, and spaces (parts created bydirecting a relatively low-power energy to mark-recorded parts to changethem to crystallized parts) and associates the edge positions (bothends) of each mark with information. Unless the relative positions ofthe edges change, this method retains information even if marks andspaces are reversed. Therefore, even if the polarity is changedalternately, no problem is generated. The method repeats the cycle inwhich melted parts are crystallized the next time information isrecorded, thus minimizing the deterioration in the reproduced signalcaused by the recording film flow.

[0008] The two methods described above, which are very excellenttechnologies, are employed as the standard of the 2.6 GB DVD-RAM and the4.7 GB DVD-RAM.

SUMMARY OF THE INVENTION

[0009] The prior art methods described above are very excellent. As amatter of fact, recording the same pattern of information on a 2.6 GBDVD-RAM in the method described above, if repeated about 100,000 times,gives the practically usable reproduced-signal quality. However,recording the same pattern of information on a 4.7 GB DVD-RAM in themethod described above, if repeated several thousand times, results in15% or higher jitters in the reproduced signal, possibly givingpractical inconvenience. The investigation made by the inventor and thecolleagues reveals at least two causes for this problem. One cause isthat the amplitude of the signal reproduced from the shortest mark onthe 4.7 GB DVD-RAM is 10 dB or lower than that of the 2.6 GB DVD-RAM.This is because the shortest mark of the 2.6 GB DVD-RAM is about 0.6microns and the shortest mark of the 4.7 GB DVD-RAM is about 0.42microns, about ⅔ times shorter than that of the 2.6 GB DVD-RAM. As aresult, when the thickness of the recording film changes as describedabove, the central amplitude level of the reproduced signal and thevariation in the amplitude largely exceed the allowable range on arelative basis.

[0010] Another cause is that, even if one of the above two methods isused, one sector may include a part which is thicker or thinner than theallowable range. A careful study indicates that the flow direction ofthe recording film depends on the length of a recorded mark. That is, inpart A, which is a part of the mark strings of a recording pattern(mark-space arrangement in one sector) in a sector, where there are many3T marks, the recording film flows in the beginning-to-end direction ofthe sector. On the other hand, in part B where there are many 4T-14Tmarks, the recording film flows in the end-to-beginning direction incontract to the part where there are many 3T marks. As a result,depending upon the positional relation between part A and part B, thethickness of the recording film exceeds the allowable range (becomesthick or thin) in the boundary between part A and part B.

[0011] Therefore, it is a first object of the present invention toprovide an information recording method and an information recordingapparatus, as well as an information recording medium, that do notgenerate an area where the thickness of the recording film does notexceed the allowable range and that minimizes the change in the centralamplitude level of the reproduced signal and in the amplitude of thereproduced signal even if information is re-written more than tens ofthousands times.

[0012] In addition, even if the above problem is solved, the thicknessof the recording film may exceed the allowable range in the beginningand end of a sector and that part of the sector may largely degrade thereproduced signal. This condition occurs when the recording film flowmay be suppressed partially but not in the whole sector. That is, whenthere is an average recording film flow in the whole sector (the amountof beginning-to-end direction flow of a sector does not match that ofthe opposite direction flow), the thickness of the recording filmexceeds the allowable range in a part near the beginning or the end ofthe sector.

[0013] Therefore, it is a second object of the present invention toprovide an information recording method and an information recordingapparatus, as well as an information recording medium, that do notgenerate, in the beginning or end area of a sector, an area where thethickness of the recording film exceeds the allowable range and thatminimize the change in the central amplitude level of the reproducedsignal and in the amplitude of the reproduced signal even if informationis re-written more than tens of thousands times.

[0014] (1) According to one aspect of the present invention, there isprovided a method for recording information for use with an informationrecording medium on which a relatively-moving energy beam strikes tomelt a recording film and to record marks corresponding to information,the method comprising a first step for recording a mark string of atleast one dummy pattern in a predetermined position before a second stepfor recording a mark string of a recording pattern corresponding tooriginal information in the predetermined position.

[0015] This method records a mark string of a dummy pattern differentfrom that of an original pattern in the first step even when a markstring of the same original pattern must be recorded repeatedly in apredetermined position. This reduces the possibility that an area wherethe thickness of the recording film is changed is generated. However,even when information is recorded in the method described above, areproduced signal degradation may occur in the beginning and end of asector. In that case, the following information recording method shouldbe used.

[0016] (2) According to another aspect of the present invention, thereis provided the method for recording information described in (1)wherein the melting causes the recording film to flow in a relativemoving direction of the information recording medium and the energy beamor in an opposite direction and the flow direction is changed inresponse to the mark string of an original pattern corresponding to theoriginal information and/or the mark string of the dummy pattern andwherein, in the first step, the mark string of the dummy pattern whoseaverage recording film flow direction is different from that of theoriginal pattern recorded in the second step is recorded at least beforethe second step.

[0017] This method prevents an average recording film flow in the wholesector, minimizing the amount of degradation of the reproduced signal inthe beginning and end of a sector. For example, when the recording of anoriginal pattern causes the recording film to flow from the end to thebeginning of the sector in the second step, the mark string of a dummypattern causing the recording film to flow from the beginning to the endshould be recorded in the first step. In addition, recording a markstring of two dummy patterns, as described below, allows the recordingfilm flow direction to be controlled more precisely.

[0018] (3) According to another aspect of the present invention, thereis provided the method for recording information described in (1)wherein the melting causes the recording film to flow in a relativemoving direction of the information recording medium and the energy beamor in an opposite direction and the flow direction is changed inresponse to the mark string of the dummy pattern and wherein, in thefirst step, the mark strings of at least two dummy patterns are recordedat least before the second step, at least two dummy patterns havingdifferent average recording film flow directions.

[0019] When doing mark edge recording, a mark string of recordingpatterns corresponding to information including marks with differentlengths is recorded. The inventor and the colleagues have revealed that,in such a case, the recording film flow direction depends on the marklength and that the recording film flows from the beginning to the endof the sector or from the end to the beginning of the sector dependingupon the mark length. In addition, they have revealed that averagerecording film flow direction depends on the existence probability ofmarks of various lengths. Furthermore, they have revealed that therecording film flow direction may be controlled more efficiently in thefirst step by separately recording a dummy pattern including markscausing the recording film to flow from the beginning to the end of thesector and a dummy pattern including marks causing the recording film toflow from the end to the beginning of the sector. That is, the followinginformation recording method is excellent.

[0020] (4) According to another aspect of the present invention, thereis provided the method for recording information described in (3)wherein, in the second step, the information is recorded on theinformation recording medium as a plurality of marks each with its ownlength and a plurality of spaces (areas between two marks) each with itsown length, the melting causes the recording film to flow in therelative moving direction of the information recording medium and theenergy beam or in the opposite direction, and the flow direction ischanged in response to the mark length and wherein, in the first step,the mark strings of at least two dummy patterns are recorded, each ofthe mark strings including a first mark group causing the recording filmto flow in the relative moving direction and a second mark group causingthe recording film to flow in an direction opposite to the relativemoving direction.

[0021] It is desired that the mark string of a dummy pattern be recordedthree or four times immediately before the mark string of an originalpattern is recorded. However, if the time required for the first stepexceeds the allowable range, the mark string of a dummy pattern may berecorded once or twice immediately before the mark string of an originalpattern is recorded. In this case, because the dummy patterns arelimited to one or two types, they may be randomly or sequentiallyselected from several types of dummy patterns and recorded.

[0022] (5) According to another aspect of the present invention, thereis provided the method for recording information described in (1)wherein there are plurality of mark strings of dummy patterns and, fromthe mark strings of the plurality of dummy patterns, the mark strings ofdummy patterns are selected randomly or sequentially for recording inthe first step.

[0023] In the case of 4.7 GB DVD-RAM, for example, there is an area,such as the defect management area, where the original pattern is likelyto be the same in most cases. Therefore, it is more efficient to use themethod described above only when information is recorded in such anarea.

[0024] (6) According to another aspect of the present invention, thereis provided the method for recording information described in (1)wherein the predetermined position is a non-user data area such as adefect management area and a user data management area.

[0025] The first mark group and the second mark group may depend on thestructure of the information recording medium or on the modulatedwaveform (recorded waveform) of the energy beam intensity for recordingmarks. In such a case, dummy pattern information and/or recordingwaveforms suited for the information recording medium should be recordedon the information recording medium as described below.

[0026] (7) According to another aspect of the present invention, thereis provided the recording information medium for use in the methoddescribed in (1), wherein the medium has an area where information onthe dummy pattern is recorded.

[0027] To implement the method for recording information described in(1), an apparatus for recording information described below is suitable.

[0028] (8) According to another aspect of the present invention, thereis provided an apparatus for recording information for implementing themethod for recording information described in (1), comprising an energybeam generator; an information recording medium moving unit whichrelatively moves the information recording medium and the energy beam;and a dummy pattern generator which generates the dummy patterns for usein the first step.

[0029] (9) According to another aspect of the present invention, thereis provided the apparatus for recording information described in (8),further comprising a dummy pattern selector which randomly orsequentially selects the dummy patterns generated by the dummy patterngenerator.

[0030] (10) According to another aspect of the present invention, thereis provided the apparatus for recording information described in (8),further comprising a dummy pattern reproducer which reproduces dummypattern information recorded on the information recording medium; and adummy pattern transmitter which transmits the dummy pattern informationto the dummy pattern generator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a block diagram showing the overview of an informationrecording apparatus used in an embodiment of the present invention.

[0032]FIG. 2 is a diagram showing the relation between reproduced signaljitters and the cycles of specific pattern recording is recorded wheninformation is recorded in the conventional method.

[0033]FIG. 3 is a diagram showing how a recording film flow depends onmark lengths.

[0034]FIGS. 4A and 4B are diagrams showing the distribution of thelengths of marks in a sector.

[0035]FIG. 5 is a diagram showing how jitters are reduced by a dummyrecording method in the embodiment of the present invention.

[0036]FIG. 6 is a diagram showing how the degradation of reproducedsignals in the beginning and end of a sector is reduced by the dummyrecording method used in the embodiment of the present invention.

[0037]FIG. 7 is a diagram showing how the degradation of reproducedsignals in the beginning and end of a sector is reduced by the dummyrecording method used in the embodiment of the present invention.

[0038]FIG. 8 is a diagram showing the information recording apparatusused in the embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0039] The present invention will be described in detail using anembodiment. A method according to the present invention uses a one-beamoverwrite mode in which information is written by one beam while erasingalready-written information.

[0040] First, an optical disk (4.7 GB DVD-RAM) used in this embodimentwill be described. The 4.7 GB DVD-RAM uses a phase change recording filmon which a laser beam is stricken to heat the recording film to atemperature above the melting point to record a mark thereon.

[0041] The disk has a 35-zone user data area extending in the radiusdirection. The management areas such as Defect Management Area (DMA) arelocated in the inner and outer sides of the user data area. In theinnermost side is located the pre-pit control data area which containsinformation such as disk linear velocity speed information, recordingwaveform information, and manufacture's information. Each zone and themanagement area are each divided into 25 to 59 sectors by the pre-pitPID (Physical Identification Data).

[0042] Information was recorded on, and reproduced from, this opticaldisk with an information recording/reproducing apparatus shown inFIG. 1. The operation of the information recording/reproducing apparatuswill be described below. The motor used to record or reproduceinformation uses the ZCLV (Zone Constant Linear Velocity) method whichchanges the number of disk rotations for each zone to or from whichinformation is recorded or reproduced. The disk linear velocity is about8.2 m/s.

[0043] Information sent from external to the recording apparatus is sentto an 8-16 modulator 1-8, eight bits at a time. When recordinginformation on an optical disk 1-1, a modulation method by which eightbits of information is converted to 16 bits, that is, an 8-16 modulationmethod, is used. This modulation method records information, 3T to 14Tin mark length, on the medium, each piece of information correspondingto eight bits. The 8-16 modulator 1-8 shown in the figure performs thismodulation. The symbol T indicates the clock period at informationrecording time. In this case, T is 17.1 ns.

[0044] The digital signal, 3T to 14T in mark length and converted by the8-16 modulator 1-8, is transferred to a recording waveform generator1-6. With the high-power pulse width of about T/2, this circuitgenerates multi-pulse recording waveforms so that a low-power levellaser beam with the width of about T/2 is produced while a high-powerlevel laser beam is produced and so that an intermediate-power levellaser beam is produced while a sequence of high-power level pulsesdescribed above are generated. At this time, the high-power level of10.0 mW is used to form a recording mark, and the intermediate powerlevel of 4.0 mW to erase a recording mark. In addition, within therecording waveform generator 1-6, the 3T-14T signals are associatedalternately with 0s and 1s on a time-series basis. When the value is 0,the intermediate-power level laser power beam strikes the disk; when thevalue is 1, a laser beam to create a sequence of high-power pulse trainsincluding high-power level pulses strikes the disk. In this case, a parton the optical disk 1 where the intermediate-power level energy beam isstricken is crystallized (space). On the other hand, a part where anenergy beam to create a sequence of high-power pulse trains includinghigh-power level pulses is stricken is turned into a non-crystallinearea (mark). In addition, to form a sequence of high-power pulse trainsincluding high-power level pulses for creating a mark, the recordingwaveform generator 1-6 includes a multi-pulse waveform table. This tablecorresponds to the method (adaptive recording waveform control) in whichthe width of the first pulse and the width of the last pulse are changedaccording to the length of spaces before and after the mark. With theuse of this table, the circuit generates multi-pulse recording waveformsthat minimize the effect of thermal interference generated betweenmarks.

[0045] The recording waveform, which is generated by the recording wavegenerating circuit 1-6, is transferred to a laser driver 1-7. Based onthe recording waveform, the laser driver 1-7 causes a semiconductorlaser within an optical head 1-3 to emit a laser beam.

[0046] The optical head 1-3 installed on this recording apparatus uses asemiconductor laser with the optical wavelength of 655 nm as theinformation recording energy beam. The optical head uses an NA0.6 lensto focus the laser beam onto the recording layer of the optical disk1-1, directs the laser energy beam corresponding to the recordingwaveform described above, and melts the recording film to recordinformation.

[0047] The recording apparatus uses a method (so-called land-grooverecording method) in which information is recorded both in a groove andon a land (an area between grooves). The recording apparatus has an L/Gservo circuit 1-9 to allow tracking to be selected for a land and agroove. The optical head 1-3 is used also to reproduce recordedinformation. That is, the optical head directs an energy beam to arecorded mark to detect a light reflected from a mark area and a lightreflected from a non-mark area to obtain the reproduced signal. Theamplitude of the reproduced signal is amplified by a pre-amplifiercircuit 1-4 and then transferred to an 8-16 demodulator 1-10. The 8-16demodulator 1-10 converts information from each 16 bits to 8-bitinformation. The above operation reproduces a recorded mark.

[0048] When information is recorded on an optical disk 1-1 under thecondition described above, the length of the shortest mark, 3T, is about0.42 μm and the length of the longest mark, 14T, is about 1.96 μm.

[0049] Using the apparatus described above, user information forming amark array of the same pattern was recorded many times on a 4.7 GBDVD-RAM to check how the number of jitters of the reproduced signaldepends on the number of recordings. FIG. 2 shows the result. The resultindicates that the jitter percentage is 9% or lower while the number ofrecordings is 10 or lower. However, when the number of recordingsexceeds 1000, the reproduced signal jitter percentage begins to increasesharply. When the number of recordings exceeds about 3000, thepercentage exceeds the allowable level of 12%.

[0050] To investigate the cause of the increase in the number ofjitters, each of the 3T to 11T mark repetitive patterns was recorded inone sector. After 20,000 times of recording, the degradation of thereproduced signals was measured (FIG. 3). As shown in the figure, anarea where the reproduced signal is largely degraded is found in thebeginning and the end of the repetitive pattern recording area of eachmark. For example, for the 3T mark repetitive pattern, the reflectance(signal level) of the beginning of the recording area is decreased andthe reflectance of the end is increased. In contrast to the 3T markpattern, the reflectance of the beginning of the 4T to 11T markrepetitive patterns is increased and the reflectance of the end isdecreased. This symptom indicates that the recording film is melted asthe marks are recorded and that the recording film flows. This resultsin the beginning of some areas becoming thick, and the end of some otherareas becoming thin. A high reflectance indicates a thick recordingfilm, while a low reflectance indicates a thin recording film. Thefigure also indicates that the 3T mark repetitive pattern and the 4T orlarger repetitive mark pattern differ in the direction of recording filmflow. For the 3T mark, the reflectance is increased (the recording filmbecomes thick) in the end of the recording area. This means that, whenthe 3T mark is recorded many times, the recording film flows in thedirection from beginning to end. This also means that, when the 4T orlarger marks are recorded, the recording film flows in the directionopposite to that of the 3T mark, that is, from end to beginning.

[0051]FIGS. 4A and 48 show an example of the relation between thepositions in a sector, where random pattern signals modulated by the8-16 modulator are recorded, and the lengths of marks included in thesector. As shown in the figure, the existence probability of 3T patternsis apparently low around positions-in-sector 5000T, 27000T, 28000T, and31000T but is apparently high around positions-in-sector 3000T and39000T. In such a case, the recording film flow near the beginning andthe end of those areas makes the recording film thickness larger orsmaller than the allowable range, generating jitters which largelydegrade the reproduced signal.

[0052] Conventionally, when the same pattern is recorded repeatedly in asector, the thickness of the recording film sometimes exceeds theallowable range in a particular position in the sector. This problem hasnot yet been solved completely and, therefore, the number of recordingsis significantly limited. In particular, an area for managing the userdata areas, such as the Defect Management Area (DMA), requires highreliability, because the area includes data on the destroyed areas and,at the same time, the area is a special area that is limited in size ascompared with other data areas. On the other hand, almost the same diskmanagement information is recorded at each recording time, and thesame-pattern information is recorded in the Defect Management Area veryfrequently. Therefore, the problem described above is serious. Althoughthe DVD/RAM standard defines that the mark and the space be reversedrandomly during the recording of the same digital pattern, this standarddoes not give a sufficient number of repetitive recordings.

[0053] To solve the above problem, the inventor and the colleagues haveinvented a method for recording dummy data before recording originalinformation. This recording of dummy data returns the recording film ofan area, whose thickness has been changed by a recording film flow, to acorrect state. That is, before recording original information of aspecific pattern including the same sequence of 0s and 1s, the methodrecords a pattern (dummy pattern) different from the specific pattern,once for at least several times, to distribute the above-describedchange in the recording film thickness (The dummy pattern is not asequence including only digital signal 0s). Or, this method records adummy pattern each time before recording original information to give abetter result. In addition, the inventor and the colleagues haveinvented a dummy pattern best for the dummy. The inventors andcolleagues also have invented a method for solving the degradation inthe beginning and the end of the reproduced signal that depends on theexistence probability of the marks within one sector and that aregenerated by the recording film flow within the whole sector.

[0054]FIG. 5 shows how jitters in the reproduced signals depend on thenumber of recordings when each of the 3T, 4T, 6T, 8T, 11T, and 14T markrepetitive patterns and a dummy pattern, different from the originalspecific pattern and produced by the 8-16 modulator, are recorded as thedummy pattern once before the original particular pattern is recorded.The number of recordings described above refers to the number of timesthe above specific pattern is recorded. In the conventional method inwhich only the original specific pattern is recorded, the percentage ofjitters exceeds the allowable range of 12% when the number of recordingsreaches about 3000. On the other hand, when the 4T mark repetitivepattern is used as the dummy pattern, the percentage of jitters exceedsthe allowable range of 12% when the number of recordings reaches 7000.When the dummy pattern is a 6T or larger pattern, the percentage ofjitters is as low as about 10.5% even when the number of recording is50000. This means a significant increase in the number of recordings.

[0055]FIG. 6 shows the sizes of areas in the beginning and the end of asector where a reproduced-signal degradation is generated after 50000times of recordings with or without dummy recording using the dummypatterns described above. When no dummy recording is done, the area is45 bytes which are larger than the target size of 40 bytes. On the otherhand, when dummy recording is done with the use of the 3T to 11T dummypatterns, the size of an area where a reproduced-signal degradationoccurred may be reduced to a size smaller than the target. FIG. 7 showsthe amount of reproduced-signal degradation that occurred in thebeginning and end of a sector when the frequency at which the dummypatterns, 11T and 3T, were recorded as the dummy pattern was changed.When the frequency at which the 3T pattern is used for dummy recordingis 12% or higher, the degradation in the beginning and end may bereduced to a value lower than the target. In particular, when thefrequency at which the 3T pattern is recorded is 20%, the jitters after50,000 times of recordings is 11% which is lower than the target valueof 12%.

[0056] The optimum frequency of the 3T mark described above depends onthe optical disk on which to write information. The optimum 3T patternfrequencies are shown below when the above test was made on optical diskof various structures.

[0057] Disk A: 20% (reproduced-signal degradation amount in trailingedge of sector: 36 bytes, jitter: 11%)

[0058] Disk B: 0% (reproduced-signal degradation amount in end ofsector: 40 bytes, jitter: 10%)

[0059] Disk C: 10% (reproduced-signal degradation amount in end ofsector: 40 bytes, jitter: 11.5%)

[0060] Disk D: 35% (reproduced-signal degradation amount in end ofsector: 40 bytes, jitter: 11.5%)

[0061] The recording film flow differs according to the optical diskbecause the layer structure and the recording film composition differaccording to the optical disk.

[0062] In such a case, information such as the dummy pattern type, dummypattern combination, and pattern frequency should be recorded in theareas, such as the control data area, which are allocated on the innercircumference of the optical disk.

[0063] In addition to the method in which the recording frequencies ofthe 3T pattern and the 11T pattern are changed, the use of a dummypattern in which the 3T pattern and the 11T pattern appear alternately,for example, every four bytes, gives the same result.

[0064] In such a case, the dummy pattern information should be recordedin advance in areas, such as the control data area of the optical disk,as described above. Then, the optical disk apparatus is able toreproduce the dummy pattern information from the optical disk and, basedon the reproduced dummy pattern information, to generate a dummy patternto do dummy recording detailed above.

[0065]FIG. 8 shows an embodiment of an optical disk apparatus forimplementing the present invention.

[0066] Referring to the figure, a motor 1060 turns an optical diskmedium 1000 to which an optical beam is directed by an optical head1020. To reproduce a signal, a reproduced signal processing circuit 1020amplifies and waveform-equalizes the signal received from the opticalhead 1020, and converts the signal to binary. Then, a demodulator 1030demodulates the signal to code information. The obtained codeinformation is sent to a host computer or some other unit, not shown inthe figure, via an interface circuit 1040. To record a signal, amodulator 1070 modulates code information, transferred via the interfacecircuit 1040, to 8-16 code and so on and stores the modulated code in amemory 1080. According to the stored code, a laser driver 1100intensity-modulates a laser beam and forms a mark in a specifiedposition on the optical disk medium via the optical head 1010.

[0067] In the case of a phase change optical disk, the quality of a markformed on the optical disk medium is deteriorated by rewriting the markas described above. Frequently-rewritten areas on an optical disk aremanagement information areas including the alternate informationmanagement area and the directory information area. The alternateinformation management area is allocated in the predetermined physicaladdresses on the optical disk. The location of the directoryinformation, though dependent on the logical format, is usually beginsat logical address 0. Therefore, at a recording time, an MPU 1120 checksif there is a probability that a specified logical address indicates anaddress where directory information is stored or if the alternateinformation management area must be rewritten to reflect a defect. Upondetecting such a condition, the MPU 1120 records a dummy signal beforerecording the specified information and then rewrites it.

[0068] Dummy information is recorded according to one of two proceduresdescribed below. The first procedure is as follows. The signal to beintensity-modulated by the laser driver 1100 is stored in the memory1080. Therefore, to record a desired signal on the optical disk medium,the MPU 1120 directly rewrites the contents of the memory via a controlcircuit 1050.

[0069] The first procedure always involves an overhead for transferringthe signal to the memory. To speed up the processing, the secondprocedure is used. A dummy pattern generator 1110 generatespredetermined signals, such as 3T or 11T repetitive signal patterns, ona hardware basis. A switch 1090 is provided to select one of the signalswith which to drive the laser driver 1100: the contents generated by themodulator 1070 or the signal generated by the dummy pattern generator1110. In the second procedure, the switch 1090 selects the dummy patterngenerator 1110 and drives the laser driver 1100 to record the dummysignal. Then, the switch 1090 selects the memory contents generated bythe modulator to overwrite the specified data. In case the dummy patterngenerator 1110 generates a plurality of patterns, special patterns to beused may be selected according to the frequency as instructed by the MPU1120.

[0070] The recording processing in this embodiment always requires anadditional time for recording dummy pattern signals. However, dummypattern signals need not always be recorded in both the alternateinformation management area and the directory information area. They maybe recorded only in one of the areas. In addition, even when informationmust be written at an address where dummy recording is required, whetherto do dummy recording may be decided according to the frequencyestablished by random numbers and so on. For example, dummy recordingmay be done for the alternate information management area at thefrequency of 30%.

[0071] In the embodiment of the present invention, even when a markstring of the same original pattern must be written repeatedly in apredetermined position, dummy recording is done in that position inadvance to record a mark string of a dummy pattern different from theoriginal pattern. This minimizes an area where the recording filmthickness is changed.

[0072] In addition, the method according to the present inventionprevents the recording film flow in the whole sector, minimizing theamount of degradation of the reproduced signal in the beginning and endof the sector. For example, when the recording of an original patterncauses the recording film to flow from the end to the beginning of thesector in the second step, a mark string of a dummy pattern causing therecording film to flow from the beginning to the end should be recordedin the first step. In addition, recording the mark strings of two dummypatterns allows the recording film flow direction to be controlled moreprecisely.

[0073] Furthermore, the present invention significantly increases thereliability of the system including the apparatus and the medium formultiple-time recording.

1. A method of recording information for use with an informationrecording medium on which a relatively-moving energy beam strikes tomelt a recording film and to record a mark corresponding to information,the method comprising: a first step of recording a mark string of atleast one dummy pattern in a predetermined position before a second stepfor recording a mark string of a recording pattern corresponding tooriginal information in the predetermined position.
 2. A method ofrecording information according to claim 1, wherein the melting causesthe recording film to flow in a relative moving direction of theinformation recording medium and the energy beam or in an oppositedirection and the flow direction is changed in response to the markstring of the recording pattern corresponding to the originalinformation and/or the mark string of the dummy pattern and wherein, inthe first step, the mark string of the dummy pattern whose averagerecording film flow direction is different from that of the originalpattern recorded in the second step is recorded at least before saidsecond step.
 3. A method of recording information according to claim 1,wherein the melting causes the recording film to flow in a relativemoving direction of the information recording medium and the energy beamor in an opposite direction and the flow direction is changed inresponse to the mark string of the dummy pattern and wherein, in thefirst step, the mark strings of at least two dummy patterns are recordedat least before said second step, said at least two dummy patternshaving different average recording film flow directions.
 4. A method ofrecording information according to claim 3, wherein, in said secondstep, the information is recorded on the information recording medium asa plurality of marks each with its own length and a plurality of spaces(areas between two marks) each with its own length and the meltingcauses the recording film to flow in the relative moving direction ofthe information recording medium and the energy beam or in the oppositedirection with the flow direction being changed in response to the marklength and wherein, in the first step, the mark strings of at least twodummy patterns are recorded, each of said mark strings including a firstmark group causing the recording film to flow in the relative movingdirection and a second mark group causing the recording film to flow inan direction opposite to the relative moving direction.
 5. A method ofrecording information according to claim 1, wherein there are pluralityof dummy pattern information types and, from the mark strings of saidplurality of dummy patterns, the mark strings of the dummy patterns areselected randomly or sequentially for recording in said first step.
 6. Amethod of recording information according to claim 1, wherein thepredetermined position is a non-user data area such as a defectmanagement area and a user data management area.
 7. A recordinginformation medium for use in the method according to claim 1, whereinsaid medium has an area where information on the dummy pattern isrecorded.
 8. An apparatus for recording information for implementing themethod of recording information according to claim 1, comprising: anenergy beam generator; an information recording medium moving unit whichrelatively moves the information recording medium and the energy beam;and a dummy pattern generator which generates the dummy patterns for usein the first step.
 9. An apparatus for recording information accordingto claim 8, further comprising: a dummy pattern selector which randomlyor sequentially selects the dummy patterns generated by the dummypattern generator.
 10. An apparatus for recording information accordingto claim 8, further comprising: a dummy pattern reproducer whichreproduces dummy pattern information recorded on the informationrecording medium; and a dummy pattern transmitter which transmits thedummy pattern information to the dummy pattern generator.
 11. A methodof recording information, wherein dummy patterns are recorded, once fora plurality of recordings, in an area where the same pattern is recordedrepeatedly, said area being in an information recording medium.
 12. Amethod of recording information, wherein dummy patterns and the samepattern are recorded alternately in an area where the same pattern isrecorded repeatedly, said area being in an information recording medium.13. A method of recording information according to claim 11, wherein thearea where the same specific pattern is recorded repeatedly is amanagement information area, an alternate information management area,or a directory information area.
 14. A method of recording informationaccording to claim 12, wherein the area where the same specific patternis recorded repeatedly is a management information area, an alternateinformation management area, or a directory information area.